Eukaryote DNA repair systems are important in repair of radiation and chemical damage, in mutation induction, in recombination, and probably in cancer induction and in normal DNA and RNA synthesis. The role of DNA polymerase is central to this repair and likely to be different in prokaryotes and eukaryotes. Using biochemical and genetic techniques the DNA polymerases in the fungus Neurospora crassa are being studied. Our results indicate that only one easily soluble, major DNA polymerase activity can be detected in extracts of Neurospora and that no new activities are induced by DNa damage. Research will continue on further purification and characterization of this activity and on attempts to detect, purify, and characterize any other polymerases present. To assess the role of the major soluble polymerase, temperature-sensitive mutants defective in this polymerase will be sought by examining the ability of colonies to incorporate (3H) Thymidine Triphosphate. Changes in polymerase activity with growth stage will also be examined.